The males possess musk or scent glands (Figure 1) which are 
situated in the chest region and the secretion from these glands 
has a characteristic odor which penetrates the roost. It is thought 
that as these bats enter the house belly downwards and head first 
some of this secretion adheres to the surface of the point of entry 
and this provides an olfactory recognition for the species as well 
as for sex, These stains are easily visible from the ground and are 
useful in recognizing a house occupied by bats. 
METHODS OF POPULATION ASSESSMENT r 
Routine inspections were made, varying from daily to monthly 
intervals, to collect the dead bats which resulted from insecticidal 
application and assessments were made of remaining live bats. This 
was attempted at first by endeavoring to: count individual bats 
inside the roof space; listen for squeaks and chirps which indicated 
pockets of non-visible bats; and distinguish between fresh guano 
after removing the old. However, the estimate of the bat population 
thus obtained was found to be highly inaccurate and a new method had to be 
devised. This consisted of the following procedure: Two observers with 
torchlights and tally counters were positioned outside at opposite ends 
of the house some distance from the building where they could see all 
sides and corners of the house (Figure 5) between the hours of approxi- 
mately 6 = 7 p.m., depending on the time of sunset. By way of example 
(Table I) data taken from the fifth spraying experiment clearly show 
the discrepancy between the two techniques. 
TABLE I 
COMPARISON OF OLD AND NEW METHODS OF BAT POPULATION ASSESSMENT 

Total bat population Total bat population 

before spraying after spraying (new 
Cold method) method) including dead 
House No, bats recovered 
fi 44 52 
1 10 63 
9 52 143 
3 50 94 
6 24 49 
2 20 23 
5 60 128 
260 552 
